mx20.fido.net has no NS records.
NS records for this zone are defined at fido.net.
NS records for this zone are defined at fido.net.
Question and response
Question
dig mx20.fido.net. NS
Answer
The response has no answer records.
Authority
fido.net. 600 SOA ns0.server.fido.net. hostmaster.fido.net. 2025111501 7200 3600 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0